Estimate lengths of things - math grade 2 - lesson 46 - part 2

2.TEACHER SAY: Today we are going to talk about estimating lengths and what mathematicians call benchmarks. When we estimate lengths, it is helpful to have some BENCHMARKS, or references, to help you think about the length. For example, remember yesterday when we looked at our pinky fingers? The distance across your finger is about 1 centimeter, so your pinky finger is a good benchmark for 1 centimeter.

TEACHER DO: Display the string sets so that students can see the 1, 10, 50, and 100 centimeter lengths. Consider taping them to dark construction paper and displaying the construction paper on the board. This will also help keep the strings straight so students can measure them.

TEACHER SAY: I have cut 4 pieces of string. This first one is 1 centimeter long.

TEACHER DO: Label the 1 centimeter string. Point to the 10 centimeter length of string.

TEACHER SAY: Raise your hand if you would like to come up and measure this piece of string.

STUDENTS DO: Raise hand to volunteer. Selected student measures the 10 centimeter piece of string and tells the class the measurement.

TEACHER DO: Help the student measure. Model as needed.

TEACHER SAY: Great work. This piece of string is 10 centimeters long.

TEACHER DO: Label the 10 centimeter string. Hold up the string that is 50 centimeters long.

TEACHER SAY: This piece of string is longer than 10 centimeters. In fact, it looks longer than my ruler.

TEACHER DO: Hold up a centimeter ruler and the length of string to show that the string is longer than the ruler.

TEACHER SAY: Turn to your Shoulder Partner and make an estimate of how long you think this piece of string is. When you have an estimate, give me a Thumbs Up.

STUDENTS DO: Turn to Shoulder Partner and discuss an estimated length for the string. Give a Thumbs Up when ready to share estimate. Selected students share their thinking.

TEACHER SAY: I heard some interesting estimates. We know that our string is longer than our centimeter ruler, so our estimates have to be higher than the highest number on the ruler. Let’s find out how long the string is. To do this I am going to need helpers.

TEACHER DO: Use Calling Sticks to choose helpers. Have students bring their rulers with them. (If you are using the rulers from the student book, you will need multiple helpers.)

STUDENTS DO: Selected students go to the front of the room with their centimeter rulers.

TEACHER SAY: First we have to line up the string at the zero on one of our rulers. One of my helpers will put their ruler at the end of my ruler.

STUDENTS DO: One student helper places their ruler at the end of the teacher’s ruler. Additional helpers add their rulers until they can measure the end of the string.

TEACHER DO: Model how to count using the added ruler. Have the student helpers assist you. Record the total number of centimeters for each ruler on the board, and then add numbers together.

TEACHER SAY: This string is 50 centimeters long.

TEACHER DO: Label the 50 centimeter string.

TEACHER SAY: If we are measuring something that is longer than our ruler, we can use a different tool to measure its length—a meter stick. The meter stick makes it much easier to measure the length of long things.

TEACHER DO: Show the students a meter stick. Point out the 0 at one end and the 100 at the other end.

TEACHER SAY: 100 centimeters is equal to 1 meter. One meter is exactly 100 centimeters. The meter is divided into 100 pieces, each 1 centimeter long. We abbreviate centimeter by writing cm. We abbreviate meter by writing m.

TEACHER DO: Write the abbreviation for meter on the board. Hold up the 100 centimeter length of string and point out the 10 centimeter and 50 centimeter pieces.

TEACHER SAY: We know this string is 10 centimeters long and this one is 50 centimeters long. How long do you think this last piece of string is? Turn to your Shoulder Partner and make an estimate about the length of this string. Give me a Thumbs Up when you are ready.

STUDENTS DO: Turn and Talk to Shoulder Partner to make an estimate about the length of the last piece of string. Give a Thumbs Up when ready. Selected students share their estimates.

TEACHER SAY: Good job. This last piece of string is longer than our 50 centimeter piece of string. Let’s use the meter stick to measure the longest string and see if your estimates were close.

TEACHER DO: Measure the longest string (or have a student help you measure it).

TEACHER SAY: Th e longest piece of string is 100 centimeters, or 1 meter, long.

TEACHER DO: Label the 100 centimeter string.

3.TEACHER SAY: Now we have a visual benchmark for how long a meter is. Now you are going to get some practice measuring. I am going to put you into groups and give each group a set of strings like mine.

TEACHER DO: Help students Count Off into small groups of 4 students. Give each group a set of strings.

TEACHER SAY: You will work with your group to find at least one item in the classroom that is about as long as each piece of string. Open your student book to page Lesson 46: Apply.

STUDENTS DO: Open student book to page Lesson 46: Apply.

TEACHER SAY: Th ere is a chart on this page. You will walk around the class with your group and find objects that are about as long as the strings. They can be a little shorter or a little longer. You are just finding objects that are an estimated length and using the strings to help you. When you have found an object that is 1 centimeter, write or draw it in the 1 centimeter row. Try and find one object for each length. If you have more time you can find extra objects.You will have about 5 minutes.

STUDENTS DO: Using the strings as benchmarks, find objects in the room that are about 1, 10, 50, and 100 centimeters long. Write or draw objects in student book.

TEACHER DO: Walk around the room to support students. Note who is having difficulty finding objects that are an estimated length. When Learn time is over, use an Attention Getting Signal to bring the group back.

TEACHER SAY: Nice work today finding objects in the class that are an estimated length. Bring the string sets to me and return to your seats. Keep out your student book.

STUDENTS DO: Return strings to the teacher and go back to their seats.